Asynchronous, event-driven "reactive" programming is way too hard in today's world of development tools and frameworks. The huge amount of manual and error-prone plumbing leads to incomprehensible and hard to maintain code. As we reach out to services in the cloud, asynchronous programming is the way of life, requiring a fresh look on the problems imposed by reactive programming. Centered around the concept of observable data sequences, Reactive Extensions (Rx) provides a framework that takes care of the hard parts of reactive event stream programming. Instead of getting lost in the jungle of asynchrony complexity, you now can start dreaming about the endless possibilities of composing queries over asynchronous data sources.

Rx v2.0 for the .NET Framework 4.5 based platforms and for Windows Phone 8 is built on a common set of assemblies for easy reuse of code between those target platforms, using a Portable Class Library project.